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| Book/Report | FZJ-2018-03078 |
; ;
1988
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18601
Report No.: Juel-2248
Abstract: Binary ice layers of $H_{2}O/NH_{3}, H_{2}O/CO_{2}, NH_{3}/CO_{2}$ (77 K), and $H_{2}O/CH_{4}$ (10 K) were prepared by condensing gas mixtures of defined composition onto a cold KBrplate in a cryostat at a vacuum of about $10^{-5}$ mbar. Layer thickness (up to a few jam) and composition were determined via IR-spectroscopy in transmission. It could be shown that in the $CO_{2}$ spectrum, $^{13}CO_{2}$ possessed other transmission characteristics than $^{12}CO_{2}$, most probably due to lesser amount of phonon coupling in the $^{13}CO_{2}$ case. For all systems, the condensates showed a depletion of the more volatile component with respect to the gas phase. The relative depletion was maximum for about 1:2 (heavy:light volatile) gas mixtures and more expressed for 77 Kthan for 10 K. The condensation behaviour was not always regular due to thermal effects of the warm gas and varying crystallization seed effects by impurities. The layers were stable at 10 or 77K over a period exceeding 7 h. During layer growth the composition did not change with condensation time, i.e. layer thickness. The preparation of amorphous ice mixtures is a necessessary condition for the simulation of chemical processes by solar wind and solar radiation in the surface of cometary nuclei, the ice mantles of interstellar grains and the early surface of asteroids by irradiation with low energy ions (keV) and photons. The results of the condensation studies may also help the understanding ofthe accretion of gases on grains in the protosolar nebula.
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